This invention relates to method and apparatus for the drying of relatively large pieces of food by immersing them in an air fluidized bed in which the suspended material is a granulated or powdered edible or non-toxic substance approved for use in association with foodstuffs. More particularly, the invention relates to method and apparatus for the simultaneous salting and drying of relatively large pieces of food (particularly fish and meat) by their immersion in an air fluidized bed of salt particles.
In the fish processing industry, current methods for preparing dried salted fish involve a number of separate steps which require days or even weeks to be carried out.
In the method most commonly used in the industry today, the fish to be processed are first cleaned, and then split or filleted prior to salting. The conventional process as well as that of the present invention is applicable to split fish, fish fillets, or portions of minced fish, but the following description will refer throughout to the handling of split fish.
In the typical conventional method of preparing salt fish, washed and drained split fish are first salted by hand. If a heavy salt fish is desired, alternating layers of fish and salt may be set out on flat surfaces such as pallets ("kench pickling") or, alternatively, the split fish may be covered with salt in a container and left to generate their own brine in a self-pickling process called "pickle cure". A minimum of three weeks is involved in this first stage in the preparation of heavy salt fish, during which period the fish naturally undergoes a "denaturation" or curing which is significant in achieving the ultimate desired taste of the product.
The preparation of light salt fish is conducted in the same manner as the pickle cure, but less salt is used and less time is allowed to elapse, typically five to six days, before proceeding to the next stage of processing. The next step in any of the aforesaid conventional fish salting processes is the washing of the split fish and allowing them to drain, a process known in the art as "waterhorsing". The split fish are then set out to dry on horizontal drying trays in a mechanical dryer, typically for twenty to twenty-four hours at a maximum temperature of 85.degree. F. The split fish are then press piled in order to equalize moisture distribution throughout the pieces of fish, whch vary considerably in thickness and, hence, rate of drying. After press piling, the conventional process for the salting of fish typically involves a further stage of heating at similar elevated temperatures in the mechanical dryer for a further twenty to twenty-four hours or more, followed by further press piling and, finally, weighing and packing of the dried salt fish product.
The known methods of preparing salt fish have drawbacks and disadvantages beyond the length of time required to obtain a suitable product, which can vary from about one week to several weeks. The known methods are manually oriented and are labour intensive. Each stage of the process requires workers to salt the fish, pack them, place them within mechanical dryers, and so on. The expenditure of time and labour adds to the cost of the finished product. Further, the prolonged exposure of the fish to ambient conditions at various stages of the process can result in spoilage and loss due to bacterial contamination.
It is evident that the combination and acceleration of some of the stages in the process of preparing salt fish is highly desirable in achieving financial savings through a more rapid turnover in inventory and the reduction of the labour input. However, any apparatus or process to achieve these goals must result in a commercially acceptable final product, preferably having the appearance and taste of that obtained by conventional methods.
The apparatus and process of the present invention eliminates a number of stages and a considerable portion of the time and labour entailed in conventional fish salting methods, while producing a salt fish product which is comparable to traditional light salted fish. According to the process of the invention, washed and drained split fish are put in racks which are immersed within a fluidized salt bed in a chamber for a period of only twelve to twenty-four hours, subsequently press piled once to render the remaining moisture content uniform throughout the fish, and then weighed and packed.
The salting and drying process which takes place within the fluidized salt bed effects a moisture content reduction from an initial content of about 70 percent, to a reduced value of about 42 to 45 percent, characteristic of the final moisture content of salt fish conventionally produced. However, in the conventional process this moisture reduction requires at least several days of salting, followed by two separate drying stages. Under the process of the present invention, the moisture transfer out of the fish may take place entirely during a single period of exposure to the fluidized salt bed, in which the transfer of salt into the fish is simultaneously effected. Further, the drying rate may be enhanced to an even greater degree in comparision to conventional methods, in that a higher ambient temperature may be used within the fluidized bed chamber than in the conventional mechanical dryers by reason of the greater rate of evaporation which takes place from the surface of the fish and the consequent lowered local temperature at the fish surface. Effective exposure times of about one-third as long as the post-salting period of drying in conventional dryers used in the traditional process have been achieved. Too, a considerably lower volume flow rate of heated dried air is required through the chamber of the present invention as compared with the flow rate of drying air in the conventional fish dryer, thereby further reducing the expenses of processing.